(1) Field of the Invention
The present invention relates to an image forming apparatus that receives image data from an external device such as a digital camera and forms an image, a power supply apparatus that supplies power to the external device, and a method of supplying power to the external device.
(2) Related Art
With recent widespread use of portable devices that supplies image data such as the digital camera and the PDA (Personal Digital Assistant), there has been a growing desire to print out obtained or received images as soon as possible even away from home. In order to respond to this desire, more and more places such as convenience stores are equipped with image forming apparatuses including printers.
For instance, the image forming apparatus is used in the manner described below. First, the user directly connects a device that provides image data to the image forming apparatus using a fixed cable. Note that the device that provides image data is referred to as an “external device” in this specification.
Then, the user chooses a desired image that is to be printed from a plurality of images that have been obtained by taking pictures, for instance, and transmits the image data of the chosen image to the image forming apparatus using operational buttons on the external device. As a result, image data is transmitted from the external device to the image forming apparatus via no personal computer and the image forming apparatus forms the image on one recording sheet according to the image data that has been transmitted from the external device to prints out the image.
Note that it is desirable to constantly supply power to each of the elements including a fixing unit in the image forming apparatus, and especially desirable to constantly keep the temperature of the fixing roller at a fixing temperature for speedy printing out. For this purpose, however, a large amount of power is wasted by the heater for the fixing roller and the like.
A proposed solution to this problem according to the conventional image forming apparatus is the sleep mode. More specifically, when a certain period of time has elapsed without printing, the sleep mode is applied to stop supplying power to the units including the heater where a relatively large amount of electricity is consumed. When receiving image data from the external device, the image forming apparatus cancels the sleep mode and supplies power to the units.
Meanwhile, the image forming apparatus at the convenience store is equipped with a coin box. According to the amount of money put in the coin box, the number of printings is managed. With such a coin box, the image forming apparatus directly satisfied user needs since the user operates the image forming apparatus without permission of the shop clerk. As a result, printing service at the convenience store and the like can be improved.
Although electricity is saved according to the conventional image forming apparatus, it takes a relatively long time to increase the temperature of the fixing unit to a fixing temperature since the sleep mode is canceled after receiving image data from the external device. As a result, a certain period of time elapsed before printing starts. This is inconvenient for the user.
Meanwhile, in some cases the external device stops working due to insufficient amount of electrical charge of a secondary battery of the external device, for instance, when the user forgot to recharge the battery. As a result, it is desirable that the secondary battery can be recharged away from home, for instance, at the convenience store. The conventional image forming apparatus providing the printing service cannot recharge the secondary battery. This is also inconvenient for the user.